This invention relates to a semiconductor device having a ferroelectric capacitor and its manufacturing method.
For years, there are known non-volatile ferroelectric memory for non-volatile storage of data by using spontaneous polarization of a ferroelectric capacitor. Ferroelectric random access memory is usable without a battery and operable at a high speed, its development to non-touch cards (radio frequency identification, herein after abbreviated RF-ID) is going to start, and its use in replacement of existing SRAM (static random access memory), DRAM (dynamic random access memory), flash memory, etc. and also as memory integrated with logic circuit, is hopefully expected.
A ferroelectric capacitor is typically made by using platinum (Pt) as upper and lower electrodes and a PZT (PbZr1-xTiOx) film as its ferroelectric film. For fabricating ferroelectric random access memory in an LSI process using a silicon substrate, a surface of the silicon substrate having formed transistors and other elements is covered with an insulating film such as silicon oxide film, and a lower Pt electrode, PZT film and upper Pt electrode are made by patterning, to thereby make the ferroelectric capacitor. Normally, a Ti or TixOy film, for example, is interposed as a base layer of the lower Pt electrode to improve its adherence.
It is known that, with this conventional ferroelectric capacitor, a reducing gas of hydrogen, etc. generated in a Si-LSI process invites deterioration of the ferroelectric property, that is, degradation of spontaneous polarization. As a countermeasure against characteristic deterioration of the ferroelectric capacitor due to reduction by hydrogen, there have been proposed some protection techniques for preventing entry of hydrogen, etc. into the capacitor portion. Heretofore, however, there have been no simple and reliable techniques.
Ferroelectric capacitors involve various problems, such as deterioration of the property caused by process damage, which must be removed, in addition to characteristic deterioration due to reduction by hydrogen.
For example, Japanese Patent Laid-Open Publication No. H 8-335673 discloses a method for covering a ferroelectric capacitor with a diffusion inhibiting film to prevent direct contact of the ferroelectric capacitor of PZT or other material and a SiO2 insulating film and thereby prevent mutual diffusion of elements between them. The publication indicates that TiO2, ZrO2 and Al2O3, for example, are effective as the diffusion inhibiting film. However, this publication deals with exfoliation of the capacitor ferroelectric film by mutual diffusion, and not the problem of characteristic deterioration of the ferroelectric capacitor by diffusion of hydrogen generated in the fabricating process.
On the other hand, through recent research, the Inventors have come to realize that the use of the TixOy film as the adhesion layer between the ferroelectric capacitor and the SiO2 film invites some undesirable problems, including deterioration of the ferroelectric property by diffusion of Ti into the PZT film, for example.